HISTO Lab Chap 8 : Endocrine System

MTY1208 Lab Week 12

Epithelium

can form endocrine or exocrine glands

• Form anastomosing cords interspersed between dilated blood capillaries

• Arranged as vesicles or follicles filled with noncellular materials

classification of endocrine glands based on arrangement of cells

Adrenal

Parathyroid

Anterior Part of Pituitary

endocrine glands that form anastomosing cords interspersed between dilated blood capillaries

Thyroid

endocrine gland arranged as vesicles or follicles filled with noncellular materials

Pituitary

Pineal

Thyroid

Adrenal

Parathyroid

Endocrine Pancreas

Major Glands of the Endocrine System

• Polypeptide-secreting Endocrine Glands

• Steroid-secreting Endocrine Glands

classification of endocrine glands based on the chemical nature of their hormones

Polypeptide-secreting Endocrine Glands

• secretes peptides, proteins, proteoglycans

• beta cells of pancreas

• pituitary glands or hypophysis

• thyroid gland and parathyroid gland

Steroid-secreting Endocrine Glands

• secrete steroids

• ovary

• testes

• adrenal gland

Pituitary Gland or Hypophysis

• small ovoid organ

• weighs about 0.5 g in adults and has dimensions of about 10×13×6 mm

Sella Turcica

• small cavity on the sphenoid bone in the base of the brain where pituitary gland is located

Adenohypophysis & Neurohypophysis

2 Divisions of the Pituitary Gland

Adenyhypophysis

• anterior

• releases hormones

• appears dark-stained

• derived from the oral ectoderm

• has three parts : a large pars distalis, or anterior lobe ; the pars tuberalis, which wraps around the infundibulumb and the thin pars intermedia adjacent to the posterior pars nervosa

Neurohypophysis

• posterior

• stores hormones

• appears light-stained

• retains many histologic features of brain tissue

• median eminence : a funnel-shaped extension of the hypothalamus

• consists of a large part, the pars nervosa, and the smaller infundibulum stalk, or infundibular stem and infundibular process

Median Eminence

a funnel shaped extension of the hypothalamus

Pars Distalis (Anterior Lobe)

• Irregular cords or clusters of glandular cells

• Largest part of anterior pituitary gland; accounts for 75% of the adenohypophysis

• Nearly all the hormones are secreted in this area

• Classified according to their affinity or lack of affinity for dyes

• Common stains suggest two broad groups of cells in the pars distalis with different staining affinities: chromophils and chromophobes

Chromophils and Chromophobes

common stains suggest two broad group of cells in the pars distalis with different staining affinities

Chromophils 

• Secretory cells in which hormone is stored in cytoplasmic granules

• Also called basophils and acidophils, based on their affinities for basic and acidic dyes, respectively

Pars Tuberalis

• More vascularized than pars distalis

• Smaller funnel-shaped region surrounding the infundibulum of the neurohypophysis

• Most of the cells of the pars tuberalis are gonadotrophs

Pars Intermedia

• Narrow zone lying between the pars distalis and the pars nervosa; separates adenohypophysis and neurohypophysis

• Contains basophils (corticotrophs), chromophobes, and small, colloid-filled cysts derived from the lumen of the embryonic hypophyseal pouch

• MSH (melanocyte-stimulating hormone) can be found here

Lumen of Embryonic Hypophyseal Pouch

where the small, colloid-filled cysts of the pars intermedia is derived

Acidophils

• Small, rounded cells

• Eosinophilic cytoplasm with large granules

• Most numerous in the postero-lateral portion of the anterior lobe

Somatotrophs, Mammotrophs or Lactotrophs

what are the cells under acidophils

Somatotrophs

• Most abundant cell type of anterior lobe

• Hormone is somatotropin (growth hormone); its release is stimulated by GHRH (growth hormone releasing hormone) from the hypothalamus

• Stimulates growth in epiphyseal plates of long bones via insulin-like growth factors (IGFs) produced in liver

Somatotropin

growth hormone of somatotrophs stimulated by GHRH from the hypothalamus

Mammotrophs or Lactotrophs

• Cells are few and distributed individually

• Secrete lactogenic hormone prolactin

• Promotes milk secretion

Basophils

Small, rounded, or ovoid cells with secretory granules of varying sizes

Thyrotrophs, Corticotrophs, Gonadotrophs

what are the cells under basophils

Thyrotrophs

• Secrete thyroid-stimulating hormone (TSH)

• Stimulates thyroid hormone synthesis, storage, and liberation

• Acts on thyroid follicles simulating the thyroid hormone synthesis

• TSH secretion depends on the thyroid-releasing hormone (TRH) from the hypothalamus

Corticotrophs

• Secrete adrenocorticotropic hormone (ACTH) and lipotropin (LPH)

• Stimulates secretion of adrenal cortex hormones

• Helps regulate lipid metabolism

• Controlled by corticotropin-releasing hormone (CRH) from the hypothalamus

Adrenocorticotropic Hormone (ACTH) and Lipotropin (LPH)

secreted by corticotrophs

Gonadotrophs

• Secrete follicle-stimulating hormones (FSH) and luteinizing hormone (LH)

• These hormones influence the cyclic development of ovarian follicles

• FSH promotes ovarian follicle development and estrogen secretion in women and spermatogenesis in men; LH promotes ovarian follicle maturation and progesterone secretion in women and interstitial cell androgen secretion in men

• Controlled by gonadotropin-releasing hormones (GnRH) from the hypothalamus

Follicle-stimulating Hormones (FSH) and Luteinizing Hormone (LH)

secreted by gonadotrophs

Neurophysis (Posterior Pituitary Gland)

• Store antidiuretic hormone (ADH), or vasopressin, and oxytocin (OT)

• Consists of the pars nervosa and the infundibular stalk 

• Composed of neural tissue

• Unmyelinated axons with terminal swelling called neurosecretory bodies or Herring bodies 

• Also present are highly branched glial cells called pituicytes

• Resemble astrocytes; most abundant cell type in the posterior pituitary

• Supports secretory bodies

Herring Bodies

Unmyelinated axons with terminal swelling called neurosecretory bodies or …

Pituicytes

•  highly branched glial cells

• resemble astrocytes; most abundant cell type in the posterior pituitary

• supports secretory bodies

Vasopressin or Antidiuretic Hormone (ADH)

• Released in response to increased blood tonicity, sensed by osmoreceptor cells in the hypothalamus, which then stimulates ADH synthesis in supraoptic neurons

• Increases the permeability of the renal collecting ducts to water so that more water is reabsorbed from the filtrate in these tubules and osmotic balance of body fluids is restored

Oxytocin

• Stimulates contraction of mammary gland myoepithelial cells and uterine smooth muscle

Thyroid Gland

• Located in the cervical region anterior and inferior to the cricoid cartilage of larynx

• Consists of two lateral lobes united by an isthmus

• Largest endocrine gland; weighs 25-40 grams

• Only endocrine gland in which a large quantity of secretory product is stored

• Synthesizes the thyroid hormones thyroxine (tetra-iodothyronine or T4) and triiodothyronine (T3), which help control the basal metabolic rate in cells throughout the body, as well as the polypeptide hormone calcitonin

Microscopic Appearance of Thyroid Gland

• Parenchyma is composed of 20-30 million microscopic thyroid follicles

• Follicles are lined by simple cuboidal epithelium and their lumen contains gelatinous acidophilic substance called colloid

• It is in the colloid where thyroglobulin is stored

Colloid

• Follicles of the thyroid gland are lined by simple cuboidal epithelium and their lumen contains a gelatinous acidophilic substance called …

Follicular Cells or Thyrocytes & Parafollicular Cells or C Cells

types of thyroid follicles

Follicular Cells, or Thyrocytes

• Responsible for secretion of thyroid hormones that regulate rate of metabolism in the cell

• Range in shape from squamous to low columnar

• Active glands have more follicles of low columnar epithelium; glands with mostly squamous follicular cells are hypoactive

Low Columnar

active glands of thyrocytes have more follicles of __________ epithelium

Squamous

hypoactive glands have mostly _________ follicular cells

Parafollicular Cells, or C Cells

• Occur singly in small groups beneath the principal cells

• Responsible for secretion of calcitonin that lowers the concentration of calcium in the body by suppressing bone resorption

• Derived from the neural crest; somewhat larger than follicular cells and stain less intensely

Calcitonin

•  lowers the concentration of calcium in the body by suppressing bone resorption

• triggered by elevated blood Ca2+ levels, and it inhibits osteoclast activity, but this function in humans is less important than the roles of parathyroid hormone and vitamin D in the regulation of normal calcium homeostasis

Neural Crest

parafollicular cells of the thyroid gland is derived from the _________

Parathyroid Glands

• Four small, ovoid bodies located at the posterior surface of the thyroid glands

• Weigh 25-50 mg each

• Derived from the embryonic pharyngeal pouches

Parathyroid Hormone (PTH)

• Important regulator of blood calcium levels

Chief Cells and Oxyphil Cells

2 types of cells in the parathyroid gland

Chief Cells

• Secrete parathyroid hormone

Oxyphil Cells

• Much larger than the principal cells and are characterized by very acidophilic cytoplasm filled with abnormally shaped mitochondria

• More commonly in older individuals

Adrenal Gland

• Paired organs lying near the superior poles of the kidneys, embedded in the pararenal adipose tissue and fascia

• Flattened triangular structures with a half-moon shape, about 4-6-cm long, 1-2-cm wide, and 4-6-mm thick in adults; weigh about 8 g combined

Thick, yellow outer cortex

Thin, reddish-brown inner medulla

fresh suction of adrenal shows …

Adrenal Cortex

• Makes up 80-90% of the gland

• Arise from mesoderm

Zona Glomerulosa

• Thin outer layer beneath the capsule

• Consists of closely packed, rounded or arched cords of columnar or pyramidal cells in an acinar arrangement with many capillaries

• Steroids made by these cells are called mineralocorticoids because they affect uptake of Na+, K+, and water by cells of renal tubules

• Principal product is aldosterone, the major regulator of salt balance

Zona Fasciculata

• Intermediate or middle layer

• Pale-staining layer

• Consists of long cords of large polyhedral cells, one or two cells thick, separated by fenestrated sinusoidal capillaries

• These cells secrete glucocorticoids, especially cortisol, which affect carbohydrate metabolism by stimulating gluconeogenesis in many cells and glycogen synthesis in the liver

Zona Reticularis

• Innermost layer 

• Consists of smaller cells in a network of irregular cords interspersed with wide capillaries

• The cells are usually more heavily stained than those of the other zones because they contain fewer lipid droplets and more lipofuscin pigment

Mineralocorticoids, Glucocorticoids, and Androgens

3 Classes of Steroid Hormones in the Adrenal Cortex

Mineralocorticoids

• Principal hormone is aldosterone

• Secreted by zona glomerulosa

• Control body fluid volume by increasing the reabsorption of sodium by kidney

Glucocorticoids

• Principal hormone is cortisol

• Secreted by zona fasciculata

• Affects the metabolism of carbohydrates, proteins, and fats

• Affect carbohydrate metabolism by stimulating gluconeogenesis in many cells and glycogen synthesis in the liver

Androgens

• Secreted by zona reticularis

• Produced in small quantity

• Of little physiologic significance in normal adults

Adrenal Medulla

• 10-20% of gland

• Arises from the ectoderm

• Secrete catecholamines

• Epinephrine and Norepinephrine 

• Both hormones stimulate glycogen breakdown, elevating blood glucose levels

• Large, pale- staining epithelioid cells arranged in rounded clusters or short cords and supported by a reticular fiber network

• Cells are believed to be modified postganglionic sympathetic neurons

• Secretory activity under the control of the nervous system

Epinephrine

• 80% of the catecholamine secreted from the adrenal medulla

• Increases alertness in brain

• Increases heart rate, dilates bronchioles, and dilates arteries of cardiac and skeletal muscle

Norepinephrine

• Increases blood sugar levels to provide more energy in our body

• In liver, it stimulates release of glucose, which serves as the energy source

• Constricts vessels of the digestive system and skin, increasing blood flow to the heart, muscles, and brain

Pineal Gland, or Epiphysis Cerebri

• Flattened conical organ approximately 5-8 mm by 3-5 mm and 120 mg

• Develops from neuroectoderm in the posterior wall of the third ventricle and remains attached to the brain by a short stalk

• Located at the roof of diencephalon

• Well-developed in children

• Regulates the daily rhythms of bodily activities

• Covered by connective tissue of the pia mater, from which septa containing small blood vessels emerge and subdivide variously sized lobule

Pinealocytes and Interstitial Glial Cells

2 Types of Cells in Pineal Gland

Pinealocytes

• Prominent and abundant secretory cells 

• Slightly basophilic cytoplasm and irregular euchromatic nuclei 

• Pale-staining 

• Secrete melatonin

Melatonin

• Activity inhibits diurnal rhythmicity related to the period of light and dark; neural control

• Resulting diurnal fluctuation in blood melatonin levels induces rhythmic changes in the activity of the hypothalamus, pituitary gland, and other endocrine tissues that characterize the circadian (24 hours, day/night) rhythm of physiological functions and behaviors

Interstitial Glial Cells

• Modified astrocytes with smaller, denser, more elongated nuclei

• Usually found in perivascular areas and between the groups of pinealocytes

Brain Sans, or Corpora Arenacea in Pineal Body

• Calcified extracellular concretions in the intercellular process

• Consist of calcium and magnesium salts in an organic matrix

• Radio-opaque

• Atrial Natriuretic Peptide (ANP)

• Gastrin

• Secretin

• Erythropoietin

• Leptin

Other Endocrine Products

Atrial Natriuretic Peptide (ANP)

• heart

• stretching atria of the heart

• Kidney : inhibits Na+ ion reabsorption and renin release

• Adrenal Cortex : inhibits secretion of aldosterone decreasing blood volume and blood pressure

Gastrin

• stomach

• for food

• Stomach : stimulate glands to release HCl

Secretin

• duodenum

• food, especially fats

• Pancreas : stimulate release of bicarbonate-rich juice

• Liver : increase release of bile

Erythropoeitin

• kidney

• hypoxia

• Bone Marrow : stimulate production of RBC

Leptin

• adipose tissue

• fatty foods

• Brain : suppresses appetite and increase energy expenditure